feat: Add stash key bindings and display

[EldoDebug]

Prompts can now be stashed without opening the command palette. Furthermore, stashed items now appear above the input field, just like in Claude Code

https://github.com/user-attachments/assets/31c66dd5-1cae-4336-a1a9-3143df3f694b

[github-actions[bot]]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions[bot]]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found